Sterols are a diverse group of lipids, many of which are found in appreciable quantities in animal and vegetal tissues. Sterols may include one or more of a variety of molecules belonging to C27-C30 crystalline alcohols, having a common general structure based on the cyclopentanoperhydrophenanthrene ring (also called sterane). In the tissues of vertebrates, the main sterol is the C27 alcohol cholesterol. There are a variety of other naturally-occurring animal sterols, such as lanosterol (a C30 compound) and 7-dehydrocholesterol, which are illustrative of the structural similarities of sterols. The nomenclature of sterols is based on the numbering of the carbons as exemplified below for cholesterol:

Sterols are also found in plants. The denomination “phytosterol” has been used for sterols of vegetal origin. Chemically, plant sterols generally have the same basic structure as cholesterol, with differences occurring for example in the lateral chain on carbon 17. Cholesterol may itself be found in plants. Representative phytosterols are compounds having 29 or 30 carbon atoms, such as campesterol, stigmasterol and beta-sitosterol (stigmasta-5-en-3beta-ol).
Steryl glycosides are sterol derivatives in which a carbohydrate unit is linked to the hydroxyl group of a sterol molecule. In plants, steryl glycosides have been found in which the sterol moiety is composed of various sterols: campesterol, stigmasterol, sitosterol, brassicasterol and dihydrositosterol. Similarly, the carbohydrate moiety may be composed of a variety of sugars, such as glucose, xylose or arabinose. Sterol glycosides may be obtained from biological sources such as plant tissues by a variety of methods (see for example Sugawara et al. Lipids 1999, 34, 1231; Ueno, et al. U.S. Pat. No. 4,235,992 issued Nov. 25, 1980). An exemplary plant sterol glycoside is beta-sitosterol-beta-D-glucoside (5-cholesten-24b-ethyl-3b-ol-D-glucoside), for which the formula is give below (also showing the structure of the acylated compound):

Acylated sterol glycosides may be formed in plants when a fatty acid is acylated at the primary alcohol group of the carbohydrate unit (such as glucose or galactose) in the steryl glycoside molecule (see Lepage, J Lipid Res 1964, 5, 587). For example, the 6′-palmitoyl-beta-D-glucoside of beta-sitosterol is reportedly present in potato tubers and the 6′-linoleoyl-beta-D-glucoside of beta-sitosterol is reportedly found in soybean extracts. Acylated steryl glucoside may be present at relatively high concentrations in a variety of vegetable parts, with the acylated form being generally more abundant that the non acylated sterol glycoside itself (Sugawara et al., Lipids 1999, 34, 1231).
Sterol glycosides also occur in bacteria. Helicobacter has for example been described as being particularly rich in cholesterol glucosides (Haque et al., J. Bacteriol 1995, 177: 5334; Haque et al., April 1996, J Bacteriol; 178(7):2065-70). A cholesterol diglucoside has been reported to occur in Acholeplasma axanthum (Mayberry et al., Biochim Biophys Acta 1983, 752, 434).
Sterols and sterol glycosides have been reported to have a wide spectrum of biological activities in animals and humans (Pegel, et al., U.S. Pat. No. 4,254,111 issued Mar. 3, 1981; Pegel et al., U.S. Pat. No. 4,260,603 issued Apr. 7, 1981) and techniques for transdermal administration of these compounds have been suggested (Walker, et al. U.S. Pat. No. 5,128,324 issued Jul. 7, 1992). It has been suggested that some plant sterols, their fatty acid esters and glucosides may be useful for treating cancers (Eugster, et al., U.S. Pat. No. 5,270,041, Dec. 14, 1993). There have been indications that sterols and sterol glycosides are generally non-toxic, or toxic only at relatively high doses while being beneficial at lower doses (Pegel, U.S. Pat. No. 4,188,379 issued Feb. 12, 1980). Some phytosterols are thought to have therapeutic effects, such as anti-tumor properties. Beta-sitosterol is categorized in the Merk Index, Tenth Edition, as an antihyperlipoproteinemic. It has been suggested that beta-sitosterol (BSS), and its glucoside (BSSG) enhance the in vitro proliferative response of T-cells (Bouic et al., Int J Immunopharmacol 1996 December; 18(12):693-700), may have other stimulatory effects as immunomodulators (Bouic et al., Int J Sports Med 1999 May; 20(4):258-62), and may therefore be therapeutically beneficial in a wide variety of diseases because of these immunostimulatory properties (Bouic and Lamprecht, Altern Med Rev 1999 June; 4(3):170-7; Bouic et al., U.S. Pat. No. 5,486,510, Jan. 23, 1996).
Cholesterol glucoside (5-cholesten-3b-ol-3b-D-glucoside) is reportedly made by human cells in culture in conjunction with a heat shock response (Kunimoto et al., an 2000, Cell Stress Chaperones; 5(1):3-7). Cholesteryl glucoside has also been reported to occur in Candida bogoriensis (Kastelic-Suhadolc, Biochim Biophys Acta 1980 Nov. 7; 620(2):322-5).
Sterol glucosides may be hydrolyzed in acid, such as in methanolic HCl (Kastelic-Suhadolc, Biochim Biophys Acta 1980 Nov. 7; 620(2):322-5). Enzymatic cleavage of the beta-glycosidic linkage may also be accomplished, for example by a beta-d-glucosidase. A thermostable beta-d-glucosidase from Thermoascus aurantiacus that hydrolysed aryl and alkyl beta-d-glucosides has for example recently been reported (Parry et al., 1 Jan. 2001, Biochem J, 353 (Pt 1):117-127). A steryl-beta-glucosidase (EC 3.2.1.104; CAS Registration No. 69494-88-8; cholesteryl-beta-D-glucoside glucohydrolase) has been identified from Sinapis alba seedlings that reportedly acts on glucosides of cholesterol and sitosterol, but not on some related sterols such as coprostanol, to hydrolyse the glucoside—producing sterol and D-glucose (Kalinowska and Wojciechowski, 1978, Phytochemistry 17: 1533-1537).
Selective neuronal cell death is the common hallmark of various neurodegenerative disorders. At least two mechanisms of neuronal death have been identified within the mammalian central nervous system: necrosis and apoptosis. Necrosis is generally characterized as a passive form of ‘accidental’ cell death that follows physical damage and is distinguished by membrane permeability changes leading to swelling of cell organelles and rupture of the plasma membrane (Simonian and Coyle, 1996). In contrast, apoptosis is generally characterized as an active form of programmed cell death involving individual cells that often remain surrounded by healthy neighbors. Apoptosis reportedly requires ATP and protein synthesis (Earnshaw, 1995) and has been characterized by cell shrinkage, membrane blebbing, and genomic fragmentation (Ellis et al., 1991; Nagata, 1997).
Both necrosis and apoptosis may be induced by stimulation of neurons by glutamate agonists acting through various glutamatergic excitatory amino acid (EAA) receptor subtypes (Choi, 1995). The actions of glutamate have been classified as either “excitotoxicity” or “excitotoxicity-independent”. Excitotoxicity is thought to involve the over-activation of target EAA receptors leading to increased ionic flux. Two main types of excitotoxicity have been described: (1) chronic/slow excitotoxicity, which is thought to result from defects in energy metabolism leading to persistent receptor activation by ambient glutamate (Zeevalk and Nicklas, 1990); and, (2) acute/fast excitotoxicity, which is thought to occur following exposure to high levels of glutamate or glutamate agonists. For example, the over-stimulation of NMDA receptors by glutamate or NMDA may result in increased calcium flux, which in turn may lead to activation of cellular proteases and the activation of other potentially harmful molecules or pathways. It has been suggested that such actions may underlie the damage caused by ischaemia and hypoxia (Choi, 1995; Meldrum and Garthwaite, 1990) or head trauma (Katayama et al., 1988).
Excitotoxicity-independent mechanisms of cell death have been shown to arise due to the accumulation of reactive oxygen species (ROS), elevation of calcium, and the loss of intracellular glutathione (GSH) (Tirosh et al., 2000). Each of these events may induce oxidative stress, described as an imbalance between oxidants (ROS) and antioxidants (GSH, GSH peroxidase, vitamins C and E, catalase, SOD, etc.) with the oxidants becoming dominant (Sies, 1991). Oxidative stress may trigger cellular necrosis (Wullner et al., 1999) as well as apoptosis (Zaman and Ratan, 1998; Hockenbery et al., 1993; Higuchi and Matsukawa, 1999; Nicole et al. 1998) and often arises due to factors leading to GSH depletion. For a number of reasons, neurons are thought to be particularly susceptible to oxidative stress, and oxidative stress-induced cell death has figured in a number of hypotheses concerning neurodegenerative diseases (see Evans, 1993; Simonian and Coyle, 1996; Palmer, 1999; Russel et al., 1999) and aging (Verarucci et al., 1999).
Toxins present in the environment may play a role in human pathology. For example, agenized wheat flour was the most common source of processed flour in much of the Western world for the first fifty years of the 20th Century (see Shaw and Bains, 1998; Campbell et al., 1950) and was later found to contain methionine sulfoximine (MSO) in high concentration. MSO induced epileptic seizures in experimental animals ((Newell et al., 1947), an action that was not understood but thought to arise due to MSO acting to inhibit the synthesis of both GSH and glutamine (Meister and Tate, 1976). Subsequent studies have revealed that MSO also has neuro-excitotoxic actions, apparently via NMDA receptor activation (Shaw et al., 1999).
The etiology of various age-related neurological diseases remains largely unknown. Sporadic forms of Alzheimer's, Parkinson's, and Lou Gehrig's disease (amyotrophic lateral sclerosis, ALS) have been linked to environmental factors that cause neuronal cell death by either by excitotoxicity or by inducing oxidative stress. The experimental and clinical literature has been taken to support a potential role for excitotoxins in some forms of neurodegeneration, notably Lou Gehrig's disease and Alzheimer's disease. In particular, abnormalities in glutamate handling/transport have been linked to ALS (Rothstein et al., 1990, 1992, 1995) and domoic acid, a kainate receptor agonist, has been shown to be causal to memory losses much like those reported in Alzheimer's disease (Perl et al., 1990). Oxidative stress has also been linked to the same diseases, particularly following GSH depletion (see Bains and Shaw, 1997). Excitotoxicity and oxidative stress may in fact be innately linked in that neural excitation, particularly over-excitation which occurs in excitoxicity, may generate free radicals acting to increased oxidative stress (Bindokas et al., 1998).
The following abbreviations may be used in the present application: ALS, amyotrophic lateral sclerosis; ALS-PDC, ALS-parkinsonism dementia complex; AMPA, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid; ATP, adenosine triphosphate; BSSG, β-sitosterol-β-D-glucoside; EAA, excitatory amino acid; GluR, glutamate receptor; GSH, glutathione; LDH, lactate dehydrogenase; MSO, methionine sulfoximine; NMDA, N-methyl-D-aspartate; ROS, reactive oxygen species; SOD, superoxide dismutase.